Minecraft is a sandbox construction game inspired by Infiniminer, Dwarf Fortress and Dungeon Keeper, and created by Markus Persson, the founder of Mojang AB. The game involves players creating and destroying various types of blocks in a three dimensional environment. The player takes an avatar that can destroy or create blocks, forming fantastic structures, creations and artwork across the various multiplayer servers in multiple game modes. And zombies.
A free, but no longer updated, version of Minecraft still exists.